DESCRIPTION (adapted from the application) Childhood obesity is a major concern since excess body weight in youth is associated with cardiovascular risk factors (e.g. elevated cholesterol) (Freedman, Lee, Byers, Kuester, & Sell, 1992), adulthood morbidity and mortality (DiPietro, Mossberg, & Stunkard, 1994) and adulthood obesity (Whitaker, et al., 1997). Physical inactivity is often identified as the primary contributor to an increase in adiposity in children (Bar-Or & Malina, 1995). Unfortunately, physical activity levels decline through childhood and adolescence (Taylor & Sallis, 1997). The causes of the decline are not known, but they may be related to changes in physical activity determinants occurring during transitional periods (e.g., school transitions). Cullen et al. (1999) found a decrease in physical activity at the time of transition out of high school. It is possible that physical activity decline during childhood may also be related to changes in physical activity determinants occurring during the elementary-middle school transition. The primary objective of the proposed study is to assess socio-environmental determinants of physical activity levels during the transition from elementary to middle school in Anglo and Mexican-American children. The specific aims of this study are as follows: 1) Assess childhood physical activity levels before and after the middle school transition; 2) document the decline of physical activity levels in Anglo and Mexican American children during the middle school transition; 3) assess environmental factors (e.g., school physical activity programs) and social (e.g., family and peer support) factors associated with the decline in physical activity levels during the middle school transition; 4) assess ethnic differences in environmental and social factors associated with physical activity among Anglo and Mexican American fifth through seventh graders; 5) assess a model of the relation among environmental and social factors and physical activity levels in fifth through seventh graders; 6) assess the relation between changes in determinants and changes in physical activity levels; and 7) assess BMI and skinfolds in Anglo and Mexican American fifth through seventh graders. Research on the determinants of physical activity among children during school transitions is in its infancy, particularly concerning minority children. Therefore, the proposed study can make a significant contribution to the current body of knowledge related to determinants of physical activity in children during school transitions. Results from this research also are needed to develop intervention programs that promote physical activity and are age-appropriate at crucial periods of times in children's lives.